Filters have been employed in a variety of applications including hydraulic systems, fuel systems, and engine lubrication systems. Such filters may generally be "spin-on" type filters and include a filter element within a can or housing having a cover or attachment plate at one end by which the filter can be screwed onto or off of a filter head. A central opening and several surrounding openings in the cover are typically provided to direct flow through the filter and filter element therein, which flow can be either an inside/out (reverse flow) or outside/in (forward flow) direction relative to the filter element. Spin-on filters are usually used only once before removal and replacement.
Fluid filters may include fuel/water separators. In a fuel/water separator, water is separated from a fuel/water mixture, in order to prevent damage to downstream engine components. Fluid filters which remove water will tend to accumulate the separated water by gravity at the bottom of the housing. The water should eventually be removed from the housing. Some models of liquid filters incorporate a mechanism to remove the water from the housing by using a pipe plug or a petcock. Typically, a threaded shaft is used to actuate these mechanisms. That is, the shaft is turned to move it linearly away from and out of the housing, until separation from the housing. They often require several turns, until separated from the housing. Often, the device begins to drain fluid as soon as it becomes unseated or loosened. The leaking fluid may run onto the operator's hand and down the arm as the device is turned the additional revolutions to the open, or separated, position. When the mechanism is to be closed, the operator is exposed to the fluid as the threaded shaft or plug is rotated several turns before it becomes closed or seated. These devices may often incorporate wrench flats or knurled covers to transmit the high amount of torque required to compress a seal to prevent leakage. A similar amount of torque may often be required to break the device free before it can be rotated by hand. Improvements are desirable.